1. Technical Field
The present invention relates to a telecommunications interface and more particularly to such an interface for insertion between an exchange line and an outgoing customer line.
2. Description of Related Art
New generations of telecommunications switching equipment are being installed which have high capacity and provide high speed broadband connections as well as point to point communication.
In the United Kingdom British Telecommunications are installing a new network which will carry broadband, voice, data and television signals over the network using internet protocol signalling. Although between switches (routers) VoIP (Voice over IP) technology will be used, legacy customer telephone equipment connected at consumer premises still requires to receive analogue signals and in particular alerting signals to activate the customer telephone equipment.
At the same time, because broadband (ADSL, DSL) signals may be carried over the local loop to the customer premises, it is essential that signalling on the local loop does not significantly increase signal to noise ratios thereon Accordingly there is a tendency to move towards balanced (analogue) ringing signals on the A & B legs of the local loop to the customer premises. These facilities and others such as responding to call answer or telephone off-hook conditions are provided by a customer line circuit connected at the switch to the A & B legs of the customer line.
In order to simplify the provision of services at the edge of the network (that is in the switch or router closest to the customer) it is desirable to minimise the number of variants of line card which need to be provided to service differing types of customer premises equipment which may be connected thereto.
It is known that a substantial number of private branch exchanges (PBX) currently in use are not designed for use with balanced ringing signals and therefore do not respond to the receipt of this kind of signalling. There are also believed to be a number of legacy telephones, facsimile machines and the like which are unresponsive to balanced ringing signals.
This problem arises not only in the United Kingdom but also in North America where it is known that, historically, telephone network providers have used unbalanced ringing signals.